Biology Test 124

HIV attacks a specific type of immune system cell in the body. It's known as the CD4 helper cell or T-cell. When HIV destroys this cell, it becomes harder for the body to fight off other infections. When HIV is left untreated, even a minor infection such as a cold can be much more severe.

Hence, the correct option is (D).

Kohler and Cesar Milstein described the hybridoma technique for the production of monoclonal antibodies. They immortalized antibody-producing cells by fusing them with tumor cells. The method allows unlimited production of monoclonal antibodies with predetermined specificity.

Hence, the correct option is (A).

Epithelial layers contain no blood vessels, so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane. Cell junctions are well-employed in epithelial tissues.

Hence, the correct option is (A).

People with lactose intolerance are unable to fully digest the sugar (lactose) in milk. As a result, they have diarrhea, gas and bloating after eating or drinking dairy products. The condition, which is also called lactose malabsorption, is usually harmless, but its symptoms can be uncomfortable.

Hence, the correct option is (B).

During the S phase or synthetic phase of interphase, replication of DNA and synthesis of histone proteins occur. New histones are required in massive amounts immediately at the beginning of the S period of DNA synthesis to provide the new DNA with nucleosomes. At the end of the S phase, each chromosome has two DNA molecules and a duplicate set of genes. S phase occupies roughly 35 to 45 percent time of the cell cycle.

Hence, the correct option is (C).

OCT, XYL and CAM are plasmids seen in Pseudomonas putida as anti-pollutants.

The plasmids are grouped into four categories: 

1) OCT plasmid which degrades, octane, hexane and decane.

2) XYL plasmid which degrades xylene and toluene.

3) CAM plasmid that decomposes camphor.

4) NAH plasmid which degrades naphthalene.

Hence, the correct option is (B).

Succinic acid is not a ketone body.

In humans and most other mammals, acetyl Co-A formed in the liver during oxidation of fatty acids can enter the citric acid cycle or can be converted to the "Ketone bodies" (e.g., Acetone, Acetoacetate and D - β hydroxybutyrate) for export to other tissue.

Hence, the correct option is (C).

A restriction enzyme or restriction endonuclease is an enzyme that cleaves DNA into fragments at or near specific recognition sites within the molecule known as restriction sites. To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix. These enzymes are found in bacteria and archaea and provide a defense mechanism against invading viruses.

Hence, the correct option is (A).

Habitat and niche refer to a single species, ecosystems to one or more. Habitat and ecosystem are a volume within the biosphere with geographic coordinates, whereas a niche could be defined as a set of functional relationships within a habitat.

Hence, the correct option is (C).

The intermediate host and vector of African trypanosomes are species of the tsetse fly (Glossina spp.). Tsetse flies become infected when taking a blood meal containing trypomastigotes from an infected human.

Hence, the correct option is (B).